Johnstone, Renfrewshire born right half Billy Clunas played for Kilbarchan Athletic in 1917 before joining hometown Scottish League club Johnstone in 1918. He had a trial with Luton Town in 1919 before joining St Mirren in March 1921, for whom he scored 10 goals in 96 appearances before he was sold to First Division Sunderland in November 1923, making his Football League debut for Sunderland on 1st December 1923 against Huddersfield Town in a 2-1 win at Roker Park.
He went on to play eight seasons at Sunderland finishing in third place in the League Championship three times during his spell at Roker Park, in 1924, 1926 and 1927 and became the club’s captain. In 1928-29 he scored ten penalties as Sunderland finished fourth in the League. Former Sunderland captain Raich Carter hailed Clunas as the best penalty kick taker he had ever seen; Clunas only missed two in his whole career, scoring an impressive 30 spot kicks for The Wearsiders. Overall, during his time at Roker Park, he scored 42 goals in 256 League appearances and also played 16 times in the FA Cup, scoring twice. He won his first cap for Scotland against England on 12th April 1924 in a 1-1 draw at Wembley Stadium. He won a further cap for Scotland when he played in a 3-0 win over Wales at Ninian Park in October 1925, scoring the third goal.
Having lost his regular place in the Sunderland line up in November 1930, he joined Greenock Morton in 1931, for whom he scored 10 goals in 63 appearances. He subsequently played for Inverness Thistle in 1934 before his eventual retirement.